Delineating E. coli occurrence and transport in the sandy beach groundwater system by radon-222.

Fecal pollution poses a global threat to environmental safety and ecosystem, but the mechanism of microbial transport and occurrence in the beach groundwater system is still poorly explored. Here, we leveraged one-year field data of Escherichia coli (E. coli) and radon-222 (Rn) and found that E. coli occurrence and transport in the sandy beach groundwater system can be delineated by Rn. The underlying mechanism behind this phenomenon is due to similar half-lives of Rn and E. coli in the sandy beach groundwater system. Thus, the unique relationship between Rn and E. coli can provide additional critical context to the microbial water quality assessments and ecosystem resilience. Also, the beach aquifer in this study is found to be a vital compartment for E. coli removal. The net E. coli removal/production capacity is identified to be highly impacted by submarine groundwater discharge. Finally, a conceptual model is constructed for a better understanding of the occurrences and characteristics of E. coli and Rn at multiple spatial scales. These findings are constructive to mitigate the hazardous influences of microbe on water quality, especially in recreational sandy beaches and mariculture zones.